1. Field of the Invention
This invention relates to apparatus for improving or restoring the breathing functions of a user or patient.
2. Description of the Prior Art
A need to improve or restore the breathing functions of an individual are commonly encountered. For example, a person's (hereinafter "patient") pulmonary or breathing functions may become impaired (e.g., due to an asthma attack) or totally or partially disabled due to an accident etc. Respiratory devices are available which implement the forced ventilation of a patient's lungs based on "passive" or "active" expiration.
Respirators which are based on passive expiration typically include a source of pressurized gas containing oxygen, a face mask or an airway device and electrically controlled valves for alternatively connecting the face mask to the gas source and to the atmosphere so that the lungs are alternately inflated and deflated.
To provide active expiration, mechanical pressure may be applied on the chest or on the patient's abdomen, for example, by means of a person's hands to force air out of the lungs or the lungs may be subjected to a reduced pressure, for example, by means of a vacuum pump, to such air out of the lungs. Only trained specialists should attempt to exert mechanical pressure with his or her hands to force ventilate a patient's lungs. Inadvertent pressure on the chest or abdomen during expiration or exhalation may lead to an excessive pressure in the lungs of the patient. In addition, such a forced ventilation method can be practiced only for relatively short time periods in critical situations. Such a method is not applicable for prolonged forced ventilation of the lungs, for example, in the case of asthma or a paralysis of the breathing organs.
Subjecting the lungs to a reduced or a sub-atmospheric pressure to force air out of the lungs is not possible in all circumstances and again cannot be used for prolonged periods. Moreover, such a procedure may be dangerous with respect to certain lung diseases, which are accompanied by the loss of elasticity of the bronchi.
Bronchial walls which have become weak and flabby due to certain diseases may collapse in response to the application of a sub-atmospheric pressure to the patient's mouth leading to the well known "air entrapment" thereby increasing the effect of expiratory closing of the breathing path.
Various types of prior art apparatus for assisting or reproducing the pulmonary and/or cardiac functions of a patient are disclosed in the patent literature. See, for example, U.S. Pat. No. 2,436,853 which issued to E. D. Coleman on Mar. 2, 1948. The Coleman apparatus includes a face mask, an inflatable chest belt and a high pressure source of gas connected to the mask for supplying breathable gas under pressure to the face mask during inhalation and for supplying the same (or different) gas to the chest belt during the exhalation phase. The Coleman apparatus poses several problems. First, the patient's exhaled gas is not limited to the face mask (which does not contain inlet and outlet check valves) but must flow through an extended exhaust tube 12 and valve 14 (open only when supply valve 16 is closed). As a result a considerable volume of expired or exhaled air containing CO.sub.2 can be rebreathed by the patient. In addition, sterilization of the Coleman apparatus would be extremely difficult since the expired air is not confined to the face mask. The Coleman mechanical linkage would also be affected by gravity (rendering the orientation of the apparatus important) and subject to wear (resulting in changes in performance characteristics with use). Last, the design of the Coleman apparatus would not be compatible with portability.
Also see, U.S. Pat. No. 4,424,806 (complex electronically controlled inflatable vest and valve mechanism for feeding gas containing oxygen to an airway coupled to the patient's lungs); U.S. Pat. No. 4,945,899 (a rigid shell jacket for surrounding the patient's chest and an electronic control system for alternatively connecting the interior of the jacket to a vacuum source or to atmosphere); U.S. Pat. No. 4,397,306 (electronically controlled chest compressor and lung ventilation means); U.S. Pat. No. 4,840,167 (an electronically controlled chest compressor and ventilator for promoting blood circulation); U.S. Pat. No. 2,699,163 (a mechanical respirator with motor driven pistons for supplying air under pressure to an inflatable vest and for controlling the supply of air to a patient's lungs); U.S. Pat. No. 3,802,417 (electronic breathing activity detection system); and Russian abstract SU1069814A (artificial respiration apparatus including a thoracic cuff and solenoid operated back massage device.
There is a need for a reliable and portable respirator apparatus for improving a patient's breathing function when such functions are impaired as a result, for example, of an asthma attack and for restoring the breathing functions in extreme situations, for example, as a result of an accident.